This invention relates to an organic EL (Electroluminescence) panel and a method of manufacturing the same.
The present application claims priority from Japanese Application No. 2004-083076, the disclosures of which are incorporated herein by reference.
An organic EL panel is produced by forming surface emission elements which are organic EL devices (elements) on a substrate, and forming a displaying area by arranging one or more organic EL devices. Each organic EL device is mounted on a substrate and comprises a first electrode, an organic layer including one or more layers of organic compound materials containing at least one organic luminescent layer, and a second electrode, thereby forming a structure with the organic layer interposed between a pair of electrodes.
In such an organic EL panel, film formation areas of layers (such as organic layer) essential for organic EL device (s) are formed corresponding to single or a group of luminescent areas (which may be pixels if display is dot matrix display) to be formed on a substrate. For example, if it is desired to effect light emission of different colors in luminescent area units in order to effect a color display, it is necessary for material layers related to light emission colors to be formed by different materials in different light emission units. However, in forming films in luminescent area units, it is also possible to select luminescent areas on which film formation is performed using an identical material, by employing a film formation mask having a pattern indicating many openings corresponding to selected luminescent areas, thereby forming film formation areas corresponding to the selected luminescent areas by virtue of mask pattern.
On the other hand, in order to improve luminescent performance and to ensure various luminescent colors for organic EL devices, the above-mentioned organic layer and electrode layers are sometimes required to be formed into multi-layered structures. At this time, the foregoing film formation mask is employed to form laminated layers in the film formation areas corresponding to luminescent areas.
For example, Japanese Unexamined Patent Application Publication Hei 2002-367787 discloses an organic EL panel shown in FIG. 1A. As shown, on one surface of a substrate 1 there are formed a plurality of first electrodes 2 consisting of a transparent conductive material such as ITO. A plurality of insulating films 3 are arranged to cover the exposed portions (between every two adjacent first electrodes 2) of the substrate 1 as well as part of the periphery of each first electrode 2, thereby dividing the substrate into a plurality of small sections and thus forming a plurality of luminescent areas 45R, 45G, and 45B on the first electrodes 2. Then, a hole injection layer 40 and a hole transporting layer 41 are formed to cover the first electrodes and spaces therebetween, while areas 60R, 60G, and 60B are selected corresponding to different colors, followed by forming in the respective areas luminescent layers 42R, 42G, and 42B, electron transporting layers 43R, 43G, and 43B, and electron injection layers 44R, 44G, and 44B. Finally, second electrodes 50 are formed over these layers.
In this way, the luminescent layers 42R, 42G, and 42B, the electron transporting layers 43R, 43G, and 43B, and the electron injection layers 44R, 44G, and 44B together form the afore-mentioned organic layer in an organic EL panel, thus constituting film formation areas corresponding to the luminescent areas 45R, 45G, and 45B.
In the above-discussed prior art, if only single one luminescent area is considered, since the luminescent layer, the electron transporting layer, and an electron injection layer are formed using an identical pattern of the same film formation mask, it is preferred that the formed three layers are overlapped one upon another without any overlap deviation. However, since the film formation mask and the substrate have to be positioned relatively to each other for forming each film layer, some troubles in positioning operation will occur and thus film formation area in a certain specific layer will suffer a considerable overlap deviation, resulting in a film formation failure.
Usually, it is supposed that various film formation errors will occur in a film formation process using a film formation mask, so that the pattern of a film formation mask should be set such that the length and width of film formation area are somewhat longer than the length and width of luminescent area. However, as shown in FIG. 1B, if a certain specific layer b of laminated layers a-c is deviated from its film formation area and thus located away from a luminescent area s, trouble will occur in the luminescent state of the luminescent area s. As a result, such film formation is usually considered as a film formation failure which must be removed.
Usually, a film formation failure can be detected by an eye-inspection using a microscope or through an image processing. If an inspected state is like that shown in FIG. 1B, it is possible to judge that such a state is a film formation failure. However, it is extremely difficult to judge which layer among the laminated layers has been greatly deviated and thus is a defective layer. On the other hand, in a process of manufacturing an organic EL panel, once a film formation failure occurs at a certain step, similar failures will probably occur in later steps. Accordingly, it is extremely important to detect a specific layer in which a film formation failure has occurred, to re-check a film formation process for forming the specific layer, so as to improve the yield of manufacturing process.